Method for manufacturing a reflective surface sub-assembly for a light-emitting device

ABSTRACT

A method for manufacturing a reflective surface sub-assembly for a light-emitting device, comprising a substrate, at least one area reserved for placement of a light-emitting device assembly on the substrate, and a diffusive reflective layer applied on selected regions on the substrate, wherein if the light-emitting device assembly were placed onto the at least one area then the diffusive reflective layer would reflect photons emitted by the light-emitting device assembly is disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. §119(e), this application claims the benefit ofU.S. Provisional Application Ser. No. 61/278,575 filed on Oct. 7, 2009,the contents of which is hereby incorporated by reference in itsentirety.

BACKGROUND

1. Field

The present disclosure relates to a light-emitting device, examples ofwhich are a light-emitting diode (LED) and a laser diode (LD), and moreparticularly, to a reflective surface sub-assembly for such a device.

2. Description of Related Technology

Without any loss of generality, merely to avoid undue repetitiveness ofthe disclosure, the state of related technology is explained using anLED as a typical example of a light-emitting device.

The principle of operation of LEDs is based on a property of asemiconductor p-n junction. When a p-n junction is forward biased, i.e.,a positive voltage is applied on the p-type semiconductor and a negativevoltage is applied on the n-type semiconductor, chargecarriers—electrons and holes—flow into the junction. When an electroncollides with a hole, the electron recombines with the hole and becausethe electron falls into a lower energy level, the excess energy—equal tothe difference between the electron and hole energy levels involved—isreleased in the form of a photon. This effect is calledelectroluminescence and the color of the light is determined by theenergy gap of the semiconductor.

Because the collision between the electron and the hole is statisticalin nature, the photons will be emitted from the p-n junction in randomdirections. To improve light extraction from the p-n junction of thelight-emitting device, a layer of reflective material is applied tosurfaces that are transparent to the emitted wavelength or have poorreflectivity of the emitted wavelength in an undesirable direction ofemission. Reflectivity is characterized by a ratio of reflected toincident light. To achieve the best possible luminous efficiency,material with high reflectivity, e.g., noble metals like Pt, Au, Ag, orother materials, like Al, are used for this purpose. However, use ofsome of the materials, e.g., Pt, Au, both from the cost of the materialsand the process of applying the materials to the surfaces, arerelatively expensive. Other materials, e.g., Al, although relativelyinexpensive, require expensive polishing and always oxides in an oxygenpresent environment. However, even after extensive—andexpensive—polishing Al's reflective power is inferior to polished Ag.Additionally, although polishing increases total reflectivity, it doesso by increasing specular reflectivity. However, as discussed in greaterdetail below, the material should possess diffusive rather than specularreflectivity. Ag, preferable to Al due to its superior reflectivity, isprone to oxidation and/or tarnishing, especially when the Ag surfacecomes in contact with some of the chemicals used in light-emittingdevice manufacturing process. An example of such would be the use ofphosphors for light conversion in LEDs. Furthermore, Ag coatedsubstrates require utter moisture protection, which increases theoverall cost of an LED package, yet not always results in the desiredlevel of performance and/or stability, i.e., resistance to change ofparameters over time, of the device. For example, although allappropriate precautions have been taken during the manufacturingprocess, due to the fact that a case of the light-emitting device is nothermetically sealed against the environment in which the light-emittingapparatus is deployed, oxidation may happen over time, thus causingdeterioration of a reflectivity, uniformity of the light and otherparameters over time.

Accordingly, there is a need in the art for improvements inlight-emitting devices to increase light output, simplify manufacturingprocess, decrease cost, and provide additional advantages evident to aperson skilled in the art.

SUMMARY

In one aspect of the disclosure, a reflective surface sub-assembly forlight-emitting device according to appended independent claims isdisclosed. Preferred additional aspects are disclosed in the dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects described herein will become more readily apparentby reference to the following description when taken in conjunction withthe accompanying drawings wherein:

FIG. 1 depicts a conceptual cross section of an exemplary light-emittingdevice in accordance with an aspect of this disclosure;

FIG. 2 depicts a conceptual cross section of a substrate with adiffusive reflective layer applied on the substrate;

FIG. 3 depicts a conceptual cross section of an exemplary light-emittingdevice in accordance with another aspect of this disclosure; and

FIG. 4 depicts details of an area around a light-emitting deviceassembly, i.e., reflective layer creating a cavity.

DETAILED DESCRIPTION

Various aspects of the present invention will be described herein withreference to drawings that are schematic illustrations of idealizedconfigurations of the present invention. As such, variations from theshapes of the illustrations as a result, for example, manufacturingtechniques and/or tolerances, are to be expected. Thus, the variousaspects of the present invention presented throughout this disclosureshould not be construed as limited to the particular shapes of elements(e.g., regions, layers, sections, substrates, etc.) illustrated anddescribed herein but are to include deviations in shapes that result,for example, from manufacturing. By way of example, an elementillustrated or described as a rectangle may have rounded or curvedfeatures and/or a gradient concentration at its edges rather than adiscrete change from one element to another. Thus, the elementsillustrated in the drawings are schematic in nature and their shapes arenot intended to illustrate the precise shape of an element and are notintended to limit the scope of the present invention.

It will be understood that when an element such as a region, layer,section, substrate, or the like, is referred to as being “on” anotherelement, it can be directly on the other element or intervening elementsmay also be present. In contrast, when an element is referred to asbeing “directly on” another element, there are no intervening elementspresent. It will be further understood that when an element is referredto as being “formed” on another element, it can be grown, deposited,etched, attached, connected, coupled, or otherwise prepared orfabricated on the other element or an intervening element.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the drawings. It will be understoodthat relative terms are intended to encompass different orientations ofan apparatus in addition to the orientation depicted in the drawings. Byway of example, if an apparatus in the drawings is turned over, elementsdisclosed as being on the “lower” side of other elements would then beoriented on the “upper” side of the other elements. The term “lower” cantherefore encompass both an orientation of “lower” and “upper,”depending of the particular orientation of the apparatus. Similarly, ifan apparatus in the drawing is turned over, elements described as“below” or “beneath” other elements would then be oriented “above” theother elements. The terms “below” or “beneath” can therefore encompassboth an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis disclosure.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise,”“comprises,” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. The term “and/or” includesany and all combinations of one or more of the associated listed items.

Various disclosed aspects may be illustrated with reference to one ormore exemplary configurations. As used herein, the term “exemplary”means “serving as an example, instance, or illustration,” and should notnecessarily be construed as preferred or advantageous over otherconfigurations disclosed herein.

Furthermore, various descriptive terms used herein, such as “on” and“transparent,” should be given the broadest meaning possible within thecontext of the present disclosure. For example, when a layer is said tobe “on” another layer, it should be understood that that one layer maybe deposited, etched, attached, or otherwise prepared or fabricateddirectly or indirectly above or below that other layer. In addition,something that is described as being “transparent” should be understoodas having a property allowing no significant obstruction or absorptionof electromagnetic radiation in the particular wavelength (orwavelengths) of interest, unless a particular transmittance is provided.

FIG. 1( a) depicts a conceptual cross section of an exemplary reflectivesurface sub-assembly 100 for a light-emitting device in accordance withan aspect of this disclosure. A substantially flat substrate 102 inaddition to being a mechanical support is often used as a means for heatdissipation from the light-emitting device. When used in the latterfunction the substrate 102 is made from a material with high thermalconductivity. Such material may comprise metals, e.g., Al, Cu, Si-basedmaterials, or any other material whose thermal conductivity isappropriate for the light-emitting device in question. A person skilledin the art will appreciate that material appropriate for alight-emitting device with power dissipation of, e.g., 35 milliwatts(mW) is different than material appropriate for a light-emitting devicewith power dissipation of, e.g., 350 mW. Flatness is understood to bedifferent than roughness in the sense that flatness describesirregularities whose spacing is greater than the roughness samplinglength. A material is considered to be substantially flat if theirregularities in flatness would not cause light to be reflected by suchirregularities.

An upper face 104 of the substrate 102 does not need to be treated,e.g., by polishing, buffing, or any other process, to acquire anyspecific reflectivity. Instead, the desired reflectivity is achieved byapplying a layer 106 of a material with high reflectivity onto selectregion(s) of the upper face 104. This concept is clarified in referenceto FIG. 2. The description of like elements between FIG. 1 and FIG. 2 isnot repeated, the like elements have reference numerals differing by100, i.e., reference numeral 102 of FIG. 1 becomes reference numeral 202in FIG. 2.

Referring to FIG. 2, the upper face 204 of the substrate 202 is depictedwith roughness characterized by a parameter R_(t) _(—) _(substrate).R_(t) _(—) _(substrate) is a difference between the height of thehighest peak and the depth of the deepest valley in the upper face 204.The layer 206, applied directly on the upper face 204 of the substrate202, is depicted with an upper face 207. The variable thickness of thelayer 206 is characterized by a parameter R_(t) _(—) _(layer). R_(t)_(—) _(layer) is a difference between the upper face 207 and the depthof the deepest valley in the upper face 204. As long as R_(t) _(—)_(layer) R_(t) _(—) _(substrate), the layer 206 fills the irregularitiesin the upper face 204. In other words, the material of the layer 206builds up the substrate 202 to the level 207 of the upper face 204.Consequently, the substrate 202 has no effect on the reflectivity, whichis determined solely by the composition of the layer 206. A personskilled in the art will appreciate that although the layer 206 isapplied directly on the upper face 204 of the substrate 202, anadditional thin layer of constant thickness (not shown) essentiallycopying, therefore, not altering, the roughness of the upper face 204,can be can be applied as disclosed in greater details below.

It is well known to person skilled in the art that an expense offabrication increases with decreased surface roughness, an appropriatechoice of material for layer 206 and/or technology for application oflayer 206 directly on the upper face 204 of the substrate 202 willaffect the required roughness. In one aspect the upper face 204roughness is between 0.05 and 5 microns.

Referring back to FIG. 1( a), a material is considered to be of highreflectivity, if a total reflectivity of the resulting layer 106 isgreater than or equal to 75%. As discussed in greater detail below, thematerial for the layer 106 should also possess diffusive rather thanspecular reflectivity. Out of the at least 75% total reflectivity, atleast 50% should be diffusive reflectivity. Of course, the higher thepercentage of diffusive reflectivity, the better the luminousefficiency; thus materials with 70% of total reflectivity, or nearly100% total reflectivity are preferable. Additional desirable propertiesof the material for layer 106 would be, e.g., non-oxidative surface, lowcost, and ease of application on the substrate.

The region(s), to which the layer 106 is applied, are selected inaccordance with determined placement of light-emitting deviceassembly(ies) 108 on the substrate 102, so that the photons emitted formthe light-emitting device assembly(ies) 108 in undesirable directionsare reflected from the layer 106. The placement of the light-emittingdevice assembly(ies) 108 is a design choice depending on multipleconsiderations, e.g., type of light-emitting device assembly, number andarrangement of the light-emitting device assembly(ies), thermalconductivity of the material 106, and other considerations known to aperson skilled in the art.

Accordingly, FIG. 1( a) depicts a design in which the selected region(s)do not include the region(s) that were determined to be occupied by thelight-emitting device assemblies 108 during the design. Although FIG. 1(a) depicts a plurality of n light-emitting device assemblies108(1)-108(n), the disclosure is equally applicable to a singlelight-emitting device assembly 108, i.e., considering only the part ofFIG. 1 delimited by an arrow 114.

As depicted, each light-emitting device assembly 108 comprises alight-emitting device chip 110 with a layer 112 of material with highreflectivity on the bottom of light-emitting device chip 110. In orderto avoid unnecessarily cluttering of FIG. 1, only the firstlight-emitting device assembly 108(1) is depicted with the referencenumerals 110(1) and 112(1). Such a light-emitting device assembly 108 iscommercially available for high power light-emitting devices, in whichthe layer 112 further provides a heat-sinking capability. Consequently,the layer 112 accomplishes the function of layer 106 for reflectingthose photons that are emitted with the direction towards the bottom ofthe light-emitting device chip 110, as well as providing low thermalresistance to the substrate 102.

Although in principle the layer 106 could be also applied on the regionoccupied by the light-emitting device assembly 108, this might increasethe thermal resistance between the light-emitting device assembly 108and the substrate 102. A person skilled in the art will understand thatthe material comprising the layer 112 may, but need not be identical tothe material comprising the layer 106.

In contrast, some lower power light-emitting device assemblies omit thelayer 112, thus comprising only the light-emitting device chip 110.Because, as disclosed above, the substrate 102 is not treated to acquireany specific reflectivity, loss of luminous efficiency due to absorptionof photons emitted with the direction towards the bottom of thelight-emitting device assembly may result. FIG. 1( b) depicts aconceptual cross section of an exemplary reflective surface sub-assembly100 for a light-emitting device in accordance with such an aspect ofthis disclosure. Should the potential loss of luminous reflectivity beunacceptable, the layer of the material 106 can be applied also on theregion occupied by the light-emitting device chip 110 (not shown in FIG.1). Although such a design may increase the thermal resistance betweenthe light-emitting device assembly 108 and the substrate 102, due to thelow power of the light-emitting device, the design may be preferable toan alternative, i.e., placing the light-emitting device assembly 108 onthe substrate and treating the substrate 102 under the light-emittingdevice chip 110 to provide a specific reflectivity.

The desirability of the diffusive property of the material with highreflectivity used for layer 106 will now be described in reference toFIG. 3. The description of like elements between FIG. 1 and FIG. 3 isnot repeated, the like elements have reference numerals differing bymultiple of 100, i.e., reference numeral 102 of FIG. 1 becomes referencenumeral 302 in FIG. 3.

Referring now to FIG. 3( a), a reflective surface sub-assembly 300 for alight-emitting device further comprises a case 316. The case 316 servesas means for protection from surrounding environment and may,optionally, also serve as means for focusing or diffusing the emittedphotons in desired direction. A photon 318 emitted from thelight-emitting device assembly 308(n) propagates along the path depictedby broken line arrow 320 through the medium characterized by arefraction index n₁ and reaches the case 316 made from materialcharacterized by a refraction index n₂. The difference in the refractionindexes n₁, n₂ creates a reflective interface. Depending on therefraction indexes n₁, n₂ and the angle of arrival of the photon 318with respect to a normal to the case 316 may cause the photon 318 to bereflected from the case 316. The reflected photon 318 then propagatesback and reaches the layer 106 made from material characterized by arefraction index n₃. As such the difference in the refraction indexesn_(i), n₃ creates a reflective interface and, if the layer 306 werespecularly reflective, following the law of reflection, reflects withthe angle of reflection equal to the angle of incidence towards the case316. This behavior may be repeated until the energy of the photon 318 islost.

The above-described mechanism changes with the layer of the material 306being diffusively reflective, as depicted in FIG. 3( b). Because of thegranular or uneven surface of the diffusively reflective layer of thematerial 306, the photon 318 may be reflected under a different angle,and, consequently, not be reflected back when the photon 318 reaches thecase 316 because the incident angle with the case 316 has been altered.

Referring to FIG. 1 and FIG. 3 the layer 106 (306) is depicted asabutting the light-emitting device assembly 108 (308), i.e., the areanot covered by the layer 106 (306) is equivalent to the area of thelight-emitting device assembly 108 (308). A person skilled in the artwill understand that the terms “abutting” and “equivalent” are to beinterpreted in a technical rather than a strict literal meaning, i.e.,the fit between the layer 106 (306) and the light-emitting deviceassembly 108 (308) will not have zero tolerance. However, such anon-zero tolerance will cause only negligible decrease in lightextraction due to some photons generated by the light-emitting devicechip 110 (310) being emitted in a direction allowing the photons toreach and be reflected by the upper face 104 (304) of the substrate 102(302) rather than the layer 106 (306). Nevertheless, achieving such afit may be difficult and/or expensive in a production environment.Consequently, FIG. 4 depicts an alternative arrangement. The descriptionof like elements between FIG. 1, FIG. 2 and FIG. 4 is not repeated; thelike elements have reference numerals differing by multiples of 100.

Considering FIG. 4( a), the requirement on the fit between the layer 406and the light-emitting device assembly 408 have been relaxed. Ratherthan abutting, the layer 406 extends to proximity what would be atypical dimension of the light-emitting device assembly 408, creating acavity 422. Consequently, a non-negligible decrease of luminousefficiency will be caused due to some photons being emitted by thelight-emitting device chip 410 in the direction allowing them to reachthe bottom of the cavity 422, and be thus reflected by the upper face404 of the substrate 402 rather than the layer 406. The decreasedluminous efficiency may be mitigated by other measures, e.g., polishingthe upper face 404 of the substrate 402 in at least the cavity, or by analternative aspect as depicted in FIG. 4( b).

FIG. 4( b) differs from FIG. 4( a) in that an additional layer 424 ofreflective material is added on the upper face 404 of the substrate 402to further improve light extraction by improving reflection of thephotons reaching the bottom of the cavity 422. As discussed above, theadditional layer 424 has constant thickness, thus essentially copying,therefore, not altering, the roughness of the upper face 404. Suchreflective material may be, for example, any of the above-mentionednoble metals. As depicted in FIG. 4( b), the layer 424 extends under theentire area occupied by the light-emitting device assemblies 408.Consequently, it is possible that the light-emitting device assemblies408 may comprise only the light-emitting device chip 410 since thefunction of the layer 412 is provided by the layer 424. In analternative (not shown), the layer 424 may abut the area occupied by thelight-emitting device assemblies 408, which should comprise both thelight-emitting device chip 410 and the layer 412.

A person skilled in the art will understand that what comprises anegligible decrease in light extraction is dependent on an application.Thus, for example, for an LED intended for application indication states“on” (LED emitting light) and “off” (LED not emitting light) severalpercent or perhaps even tens of percent of decrease in light extractionare negligible. On the other hand, for an LED intended for applicationin lighting, only units of percent or perhaps even less may beconsidered negligible.

Although as understood, any highly reflective material with diffusereflection satisfying the disclosed parameters may be used, theinventors discovered that good results were achieved with titanium oxideor other oxide phases or compositions such as TiO₂, Ti₂O₃, and the like.The improvement of luminous efficiency over that of related technologiesusing noble metal based coating was by 5 to 25%, depending onspecificity of the substrate/light-emitting device assembly geometry,even though titanium oxide is known to have specular reflectivityinferior to the specular reflectivity of the above mentioned noblemetals. This further confirms the importance of diffusive reflectivityinherent in, e.g., the above-mentioned titanium oxide or other oxidephases or compositions such as TiO₂, Ti₂O₃, and the like. The diffusivereflectivity is provided by the random orientation of the crystals ofthe titanium oxide or other oxide phases or compositions such as TiO₂,Ti₂O₃, and the like. In addition to high total and diffusivereflectivity, titanium oxide or other oxide phases or compositions asutilized according to this disclosure possesses many of the propertiesdesirable for material for layer 106, i.e., non-oxidative surface,diffusive reflection, relatively low cost, and the like.

Referring back to FIG. 1, different methods may be used for applyinglayer 106 directly on the substrate 102, e.g., dispersing, brushing, andthe like. However, screen-printing, which utilize well known thick filmtechnology has been found to be effective especially with regards tolayer 106 being titanium dioxide. Consequently, for the purposes ofsimplicity, the manufacturing process will be described in regards tothe titanium dioxide. However, a person skilled in the art wouldunderstand that the manufacturing process is equally applicable to othermaterials, which could comprise layer 106, in accordance with conceptsdisclosed herein. A person skilled in the art would further understandthat the term “thick-film” refers to a particular technology and is notrestricted to any particular thickness for each layer.

After the design of the light-emitting apparatus has been finished, asubstrate 102 is manufactured from the appropriate material. A stencilor a screen is then prepared with selected regions for a transfer of acurable titanium dioxide paste, which after curing will create the layer106, directly on the chosen substrate 102. Good results have beenachieved with a titanium dioxide paste composition comprising polymermatrix, titanium dioxide filler, and additional rheological additiveswhich adjust rheological properties of the paste. The additionalrheological additives comprise, e.g., silica, alumna, zinc oxide,magnesium oxide, talc, and other additives known to a person skilled inthe art, used either individually or in combination. The constitutingcomposition elements, e.g., choice of polymer, particle sizes, loadinglevel and the like, need to be optimized to assure that the rheology ofthe paste follows pseudo-plastic behavior.

Based on the foregoing requirement, in one aspect, the polymer matrixmay comprise any curable silicone ensuring a good bond of the titaniumdioxide paste with the surface of the chosen substrate 102. Preferably,polymers that possess hydride, hydroxyl or other reactivefunctionalities are selected for their superior bonding characteristics.The titanium dioxide filler may comprise particles with average sizebetween 100 nm to 20 microns, and the loading level may be between 10%to 75%, depending on specific surface area of the titanium dioxideparticles. The particle sizes and loading levels of the rheologicaladditives are selected to appropriately adjust the rheologicalproperties as disclosed above. Thus, by means of an example, the silica,e.g., untreated fumed silica, may comprise particles with average sizeof tenths of microns, and the loading level from 0% to 4%, combined withthe alumna, e.g., fumed alumina, with a loading level from 0.1% to 2%.

Once the titanium dioxide paste is prepared according to the disclosedguidelines, the titanium dioxide paste is transferred onto the screen ofthe screen printer and screen printing proceeds according to methodologyknown in the art. Thus a conventional screen printer may be used toscreen-print the titanium dioxide paste onto the chosen substrate. Upontransfer of the titanium dioxide paste on the substrate, the temperatureis kept at room temperature for a first interval. In one aspect thefirst interval is 20 minutes. The substrate with the titanium dioxidepaste thereon is then placed into an oven for pre-curing during a secondinterval. In one aspect the oven temperature is then raised to 110° C.during the second interval. In one aspect the second interval is one totwo hours. The temperature is then raised and the titanium dioxide pasteis cured at this third temperature for a third time interval. In oneaspect the third temperature is approximately 150° C. and the third timeinterval is between 2-4 hours depending on the composition of the paste.

The various aspects of this disclosure are provided to enable one ofordinary skill in the art to practice the present invention.Modifications to various aspects of a presented throughout thisdisclosure will be readily apparent to those skilled in the art, and theconcepts disclosed herein may be extended to other applications. Thus,the claims are not intended to be limited to the various aspects of thereflective surfaces for a light-emitting device presented throughoutthis disclosure, but are to be accorded the full scope consistent withthe language of the claims. All structural and functional equivalents tothe elements of the various aspects described throughout this disclosurethat are known or later come to be known to those of ordinary skill inthe art are expressly incorporated herein by reference and are intendedto be encompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

1. A method for manufacturing a reflective surface sub-assembly for alight-emitting device, the method comprising the steps of: manufacturinga substrate; predetermining at least one area reserved for placement ofa light-emitting device assembly on the substrate; and applying adiffusive reflective surface on selected regions on a substrate; whereinif the light-emitting device assembly were placed onto the at least onearea then the diffusive reflective layer would reflect photons emittedby the light-emitting device assembly.
 2. The method according to claim1, wherein the step of manufacturing a substrate comprises the step ofmanufacturing a substantially flat substrate.
 3. The method according toclaim 1, wherein the step of applying a diffusive reflective surface onselected regions on a substrate comprises the step of applying adiffusive reflective layer characterized by at least 50% diffusivereflectivity.
 4. The method according to claim 1, wherein the step ofapplying a diffusive reflective surface on selected regions on asubstrate comprises the step of applying a diffusive reflective layercharacterized by at least 70% diffusive reflectivity.
 5. The methodaccording to claim 1, wherein the step of applying a diffusivereflective surface on selected regions on a substrate comprises the stepof applying a diffusive reflective layer to fill irregularities in aface of the substrate.
 6. The method according to claim 1, wherein thestep of applying a diffusive reflective surface on selected regions on asubstrate comprises the step of applying a diffusive reflective layercomprising titanium oxide or other oxide phases or compositions.
 7. Themethod according to claim 1, wherein the wherein the step of applying adiffusive reflective surface on selected regions on a substratecomprises the step of applying a diffusive reflective layer comprisingtitanium dioxide.
 8. The method according to claim 1, wherein the stepof applying a diffusive reflective surface on selected regions on asubstrate comprises applying a paste comprising: a polymer matrix, atitanium oxide or other oxide phases or compositions filler, and arheological additive.
 9. The method according to claim 8, wherein therheological additive comprises a silica and alumna.
 10. The methodaccording to claim 9, wherein the loading levels of the paste'scomposition comprise: the titanium oxide or other oxide phases orcompositions filler in an amount of 10%-75%, the silica in an amount of0%-4%, and the alumna in an amount of 0.1-2%.
 11. The method accordingto claim 10, wherein the titanium oxide or other oxide phases orcompositions filler comprises titanium dioxide filler.
 12. The methodaccording to claim 1, wherein the step of applying a diffusivereflective surface on selected regions on a substrate comprises the stepof applying a diffusive reflective layer excluding the at least one areareserved for placement of a light-emitting device assembly.
 13. Themethod according to claim 1, wherein the step of applying a diffusivereflective surface on selected regions on a substrate comprises the stepof applying a diffusive reflective layer including the at least one areareserved for placement of a light-emitting device assembly.
 14. Themethod according to claim 1, wherein the step of predetermining at leastone area reserved for placement of a light-emitting device assemblycomprises predetermining at least one area equivalent with the area ofthe light-emitting device assembly to be placed on the at least one areareserved for placement.
 15. The method according to claim 1, wherein thestep of predetermining at least one area reserved for placement of alight-emitting device assembly comprises predetermining at least onearea greater than the area of the light-emitting device assembly to beplaced on the at least one area reserved for placement.
 16. The methodaccording to claim 1, wherein the step of applying a diffusivereflective surface on selected regions on a substrate comprises applyinga diffusive reflective surface on selected regions on a substrate byscreen-printing.
 17. The method according to claim 1, further comprisinga step of placing a light-emitting device assembly on the at least onearea reserved for placement of the light-emitting device assembly.